1. Field of Invention
This invention relates in general to supervisory functions in a communications network, and in particular to a dedicated supervisory control plane over wavelength routed networks.
2. Related Art
Optical networks are comprised of functionality providing transport, multiplexing, routing, supervision and survivability of client signals that are predominantly processed in the photonic domain. Generally, the functional architecture of optical networks includes the optical network layered structure, the client/server layer association, the network topology, and the network layer functionality. In the following description, optical signals are characterized by wavelength, or a central frequency, and may be processed per wavelength, or as a wavelength division multiplexed group of wavelengths.
The optical transport network is subdivided into independent transport layer networks where each layer network can be separately positioned in such way so as to reflect the internal structure and functionality of this particular layer network.
The layered structure of the optical transport network is comprised of the optical channel, the optical multiplex section, and the optical transmission section layer networks. The optical layer network provides end-to-end networking of optical channels for transparently conveying client information of varying format. The role of the layer network is to provide the connection arrangement for flexible network routing, the overhead processes for ensuring integrity of the optical channel specific information, as well as the optical channel supervisory functions.
The supervisory channel functions enable network level operations, administration, and maintenance (OAM) functions such as connection provisioning, quality of service (QoS) parameter exchange, optical performance monitoring, and network survivability.
The optical channel layer network provides for transport of digital client signals through an optical channel trail between access points. The characteristic information of an optical channel layer network is composed of two separate and distinct logical signals: a first data stream that constitutes the adapted information of a client layer network (customer traffic), and a second data stream that constitutes the optical channel trail termination overhead (OAM traffic). The channel trail termination overhead provides validation of connectivity integrity, assessment of transmission quality, and transmission of defect detection and indication.
“Lucent Technologies” has proposed the use of a “digital wrapper” (the TDM technology) to process optical overhead information in the digital domain. The TDM overhead information includes an indication regarding the optical performance parameters. This digital wrapper needs Optical-Electrical-Optical conversion and monitoring of the control functions must ne performed at each point of the network where traffic is added or dropped.
The drawback of this approach is the additional costs and limitations added to the implementation of the all-optical, or pure photonic switched network. It also degrades transport transparency of all-optical networking and causes increased interworking complexity for non-TDM traffic such as Gigabit Ethernet and Escon signals.
The optical transport network is designed to support the control functions, or OAM functions. The optical transport network establishes end-to-end communications, or a communications path, and supervises the integrity of network connections along the communications path. The continuity along the communications path is constantly monitored to detect loss of continuity and in the event of a signal within the data layer being interrupted, upstream and downstream network entities along the path are notified. Finally, maintenance indications are required for indicating defects in a connection which is part of the communications path.
The control functions may be used by the network operator to provide routing, grooming, performance monitoring, and/or protection and restoration. The control functions are a network priority because absent this functions there are no communications at all within the network.
Several proposals have been raised to support a control plane comprised of wavelength routing and signaling functions in an optical network. The International Telecommunications Union Working Group 15 Recommendation G872 (ITU WG 15 G872) has defined the optical supervisory channel as point-to-point link between optical transport network elements for OAM purposes. The optical supervisory channel according to ITU WG 15 G872 is a dedicated, point-to-point supervisory channel and there is no build-in routing/signaling control functionality.
The IETF “www.draft-awduche-mpls-te-optical-00.txt” has proposed the use of a separate IP network for routing/signaling control functionality. The separate IP network is needed to support optical layer network routing/signaling of control massages. This separate IP network presents cost, performance, and reliability issues similar to the actual public system telecommunications network (PSTN) signaling network. By using a separate IP network as a wavelength routing/signaling platform, the reliability of the wavelength routing/signaling functions will rely on the reliability of the IP network, which is known as having a low availability.
Accordingly, there is a need for a supervisory control plane over wavelength routed networks capable of providing simple and reliable network-wide control functionality and dynamic wavelength routing and signaling, at an affordable cost while potentially providing truly transparent performance monitoring and OAM functions for supporting all-optical networking.